From: Ross Bamford <rossrt@...>
Date: 2006-04-14T17:40:09+09:00
Subject: Re: Rubyesque way to do multiple <=>

On Fri, 2006-04-14 at 16:49 +0900, Victor Shepelev wrote:
> > >def <=> (other)
> > >  res = ComplexCustomComparator.compare(sex, other.sex)
> > >  return res if res != 0
> > >
> > >  #if they have the same sex, do other comparisons
> > >end
> > >
> > >Foooooo!
> > >
> > >How can I do the former in more elegant way?
> > >
> > >
> > 

How about something like (untested):

def <=>(other)
  [:name, :age, :sex].map do |attr,comp| 
    ComplexCustomComparator.compare(send(attr), other.send(attr))
  end.find { |e| e.nonzero? } || 0
end

Or if you have to use a different comparator for each attribute:

def somewhere_else_eg_initialize
  @comparators = [NameComparator.new, 
                  AgeComparator.new, 
                  SexComparator.new]
end

def <=>(other)
  [:name, :age, :sex].zip(@comparators).map do |attr,comp| 
    comp.compare(send(attr), other.send(attr))
  end.find { |e| e.nonzero? } || 0
end

Probably not the most efficient way (two iterations) but it should work
I think.

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk